Polyphasic in vitro characterization of the pigment-producing microfungus Rhodotorula sp. for potential application as a probiotic in mariculture

Pigment-producing microfungi represent a promising source of bioactive compounds. This study represents a polyphasic evaluation of a novel Rhodotorula paludigena (PX945103) isolate to determine its suitability as a probiotic with nutritional, functional, and biotechnological potential. The pigment producing microbe was isolated from the mangrove ecosystems of Kochi, southern India. The isolate was identified as Rhodotorula sp. based on morphological and molecular characteristics. Microbial characterization of the isolate revealed stable growth performance, with the strain producing a dry biomass of about 0.73 g/L in YEPD medium. It also synthesized pigments up to 398.7 μg/g dry weight and 1681.56 μg/L culture. The extracted pigment exhibited a λ max at 458 nm, with maximum intracellular carotenoid accumulation occurring on 5th day of cultivation. Fatty acid profiling of the Rhodotorula paludigena (PX945103) indicated PUFA content of about 28.21% of the total fatty acids. Linoleic acid and α -Linolenic acid dominated the PUFA profile accounting for 19.9 and 4.1% of the total fatty acids, respectively. Amino acid profiling of the Rhodotorula sp. revealed a lysine content of 61.86 g/kg dry weight. Incubation in simulated intestinal fluid had no significant impact on viability of the microbe. However, in simulated gastric fluid the viability of Rhodotorula sp. decreased significantly after 80 min, from 11.76 to 9.52 ± 0.14 Log₁₀ CFU/mL. A strong correlation was observed between the biomass and radical scavenging activity of the isolate (R 2 = 0.98, p < 0.0001 for DPPH; R 2 = 0.91, p < 0.0001 for ABTS). Well diffusion assay of the crude acetone extract of Rhodotorula paludigena (PX945103) was effective against pathogens, with zones of inhibition of 17.66 ± 0.44, 15.00 ± 0.57, 25.30 ± 0.33 and 15.00 ± 0.57 mm for V. parahaemolyticus, V. alginolyticus, V. harveyi and E. coli , respectively indicating considerable antibacterial effects. This study establishes a foundational framework for advancing Rhodotorula sp. as a promising next-generation probiotic microfungus.